FACTORS RELATED TO JELLYFISH OCCURANCE

A)Zooplankton

Plankton is defined as all those organisms suspended in free water (Barnes, 1980). The plankton comprises of aquatic organisms which drift passively and have limited ability to move contrary to the movement of the water mass. Zooplankton is the animal portion of the plankton (Ismail, 1998). Zooplanktons are referred as microscopic aquatic organisms that have less or no resistance towards water current. Majority of them are microscopic, unicellular or multi-cellular forms with size ranging from a few microns to a millimeter or more (Barnes, 1980).

Therefore, zooplanktons play an important role in the study of fauna biodiversity of aquatic ecosystems. They include representatives of almost every taxon of the animal kingdom and occur in the pelagic environment either as adults (holoplankton) or eggs and larvae (meroplankton) (Raymont, 1983). Holoplanktons are plankton that spent their entire life drifting about in water as plankton, while meroplankton spent only part of their life as plankton (Ismail, 1998). Holoplanktons include the pelagic copepods, chaetognaths, some medusae and pteropods. Larval stages of many starfish, worms, bottom-living fish, crabs, and prawns are include as mesoplankton.
Zooplanktons provide a major role in the marine food web from primary producer to higher levels of trophic links. Many zooplanktons eat phytoplankton, and are in turn preyed upon by fish larvae and many adult planktivorous fish (Ismail, 1998). Conversely, certain zooplankton groups (e.g. medusae) also prey on fish eggs and larvae. Due to their intermediate position in the food web between primary producers and predators, zooplankton serves as a link between bottom-up climate-related control of phytoplankton and fish.

The distributions of zooplankton are usually influenced by the environmental factors, availability of food source and the interaction between them. Some of the species of zooplankton are found differently according to latitude variation. The presence of available food supply plays a great influence on its distribution. The composition of zooplankton is high with the presence of phytoplankton or small zooplankton that is fed by larger sizes of predatory zooplankton. Competitions for food, space, and breeding partner between zooplankton which occupied the same habitat also affect its distribution.

B)Phytoplankton

Marine phytoplankton is a microscopic single-cell plants which are the most abundant planktonic plant in the sea. It is able to absorb water and captures light energy from the sun, thus converting it into oxygen and nutrients through photosynthesis (Zeitzschel, 1970). In addition to light and oxygen (O2), they require basic simple inorganic chemical nutrients, such as phosphate (PO4) and nitrate (NO3). They also require carbon in the form of carbon dioxide (CO2). They obtain the nutrients which are released after the decomposition of waste and dead tissue by bacteria. Phytoplankton creates materials such as carbohydrates, fats, and proteins from carbon dioxide, water and inorganic chemical nutrients through photosynthesis.

Phytoplankton belongs to the groups of non-flowering plants such as Cyanochloronta (blue-green algae), Rhodophycophyta (red algae), Chlorophycophyta (green algae), Euglenophycophyta (euglenoid), Phaeophycophyta (brown algae), Chrysophycophyta (golden and yellow-green algae including diatoms), and Pyrrophycophyta (dinoflagellates), Cryptophycophyta (cryptomonads). Dinoflagellates are more diverse in the marine environment whereas green and blue-green algae constitutes greater in freshwater environment. On the other hand, diatoms are more common in both environments (Harris, 1986).

According to Lund (1954-55), various factors affect the distribution of phytoplankton such as the concentration of major ions (C, N, P, S, and Si) and weather condition. Alongi (1998) verifies that nutrient availability depends on physical force such as monsoons. After monsoon season, a maximum mixing occurs between seawater and freshwater, thus producing high concentration of nutrients. Therefore, the situation promotes higher production of phytoplankton. During pre-monsoon season, nutrient depletion occurs due to less intensity of mixing between freshwater and seawater, therefore causing low productivity. The productivity is much lower during monsoon season because of the effect of water turbulence that cause greater turbidity and low level of light penetration.

Phytoplankton analysis is important for this project because it helps researchers to correlate the phytoplankton and jellyfish indirectly based on its biomass and composition. We will not be able to identify the primary cause (instead of zooplankton abundance) of sudden jellyfish bloom if the analysis is not done. As a result, the analysis will provide one of the important evidences responding to the unpredictable bloom of jellyfish or other aquatic organisms.

C) Water Quality

According to Purcell et al., 2007 and Mills, 2001, the jellyfish blooms may be triggered by the warming of sea temperature due to global climate change or power plant effluent. In temperate area, the jellyfish usually increased their asexual production of polyps bud and new jellyfish during warm temperature while in tropical area, the jellyfish production may occur all year (Lucas, 2001). Thus, the jellyfish blooms may occur all the time at the tropic area despite of the season.

Eutrophication may also increase the abundance of jellyfish in that area. The eutrophication occurs as a result of increased mineral nutrients concentration (primarily nitrogen and phosphorus), change in nutrients ratios and increase in turbidity, where there are human activities at the coastal area (Howarth, 2002; Arai, 2001). Eutrophication can occur because of natural processes such as river inflow and upwelling, but anthropogenic cause has become the present concern (Arai, 2001). Nutrients are increasing in water bodies as the result from addition of sewage, deforestation, fertilizer usage on adjacent land and reactive nitrogen emitted to the atmosphere during fossil fuel combustion. The increasing of nutrients in water column may lead to greater biomass at all trophic levels and increasing the food source for jellyfish polyps (Daskalov, 2002; Purcell et. al., 1999). Besides that, the jellyfish will also increase their asexual production as well as sexual production (Stibor & Tokle, 2003; Lucas, 2001 see Purcell et. al., 2007). Eutrophication also can caused complex changes in the food web. It may change the food path of an ecosystem towards a flagellate-based path that ends with ‘low energy’ consumers, which favors the jellyfish. This condition may occur when N:P ratios is high and could shift the phytoplankton community away from diatoms towards flagellates and jellyfish (Nagai, 2003). Furthermore, nutrient enrichment may reduce the size of zooplankton community which is detrimental to fish. This is because they are visual predators that prefer large zooplanktons. Therefore, this will benefits the jellyfish that are not visual and they can consume small or large prey.

WHAT IS JELLYFISH PROBLEM-RELATED?

Jellyfish blooms are common occurrences in many marine habitats and are important events controlling plankton dynamics in these systems (Purcell et al., 2001). The increasing of reports on human problems with jellyfish within coastal marine systems has lead to much public attention the ecological role of jellyfish (more specifically medusa of the Phylum Cnidaria: Orders Rhizostomeae and Semaeostomeae) (Whiteman, 2002; Carpenter, 2004; Hamner & Dawson, 2009).
The jellyfish existence has caused ecological and socio-economical problems. Ecologically, they will disturb the food web of the ecosystem of the invaded area since they feed on zooplankton and ichthyoplankton that is also food source for other aquatic animals i.e. fish (Purcell et al., 2007). Besides that, they might cause algae blooming due to the decreasing of zooplankton that feed on them.
In the socio-economic area, the jellyfish may interfere with tourism by stinging swimmers, fishing by clogging nets, aquaculture by killing fish in net-pens and blocking cooling-water intake screens at coastal power plants (Purcell et al., 2007; Richardson et al., 2009; Lynam et al., 2006). Since they are feeding on zooplankton and ichthyoplankton, they also have indirect effects on fisheries by becoming as the competitors of fish and eventually may decrease fish population (Purcell et al., 2007; Richardson et al., 2009). According to Purcell et al. (2007), increased jellyfish and ctenophore populations often are associated with warming caused by climate changes and possibly power plant thermal effluents. In short, the propensity of jellyfish in forming extensive nuisance blooms and their associated socioeconomic effects have largely driven the interest on jellyfish study (CIESM, 2001).

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WHAT IS JELLYFISH ALL ABOUT?

Figure 1: The life cycle of jellyfish

THE BIOLOGY OF JELLYFISH

The life-cycle of jellyfish is different among the classes. The life cycle of common jellyfish requires an alteration of generations, which they need to pass through two different body forms (SCDNR, 2009). The familiar form that usually found is the dominant medusa form, while the sessile and smaller polyp form occurs only during larval stage. Jellyfish could reproduce sexually or asexually. When they reproduce sexually, the individuals are dioecious, which it will be either male or female. After fertilization occurs, the embryo will developed either inside the female or in brood pouches along the oral arms. Then, it will develop into swimming larvae called planulae and enters the water column. Several days later, the larvae attach themselves to something firm on the sea floor (rocks, shells, etc.) and gradually transform into flower-like polyps called scyphistoma. These polyps use tentacles to feed on microscopic organisms in the water column. Polyps can reproduce asexually by producing buds or cysts that separate from the first polyp and develop into new polyps. When conditions are right, the polyps will undergo a process called strobilation, which produce a larval stage (the strobila) that resembles a stack of saucers. One by one each disc detaches from the end of the strobila and become an ephyra. It is a tiny jellyfish that resembles like the mature form. In a few weeks, the ephyra will grow into an adult jellyfish (medusa), thus completing the complex life cycle. Jellyfish normally live for a few months; however, the polyp stage may be perennial. In this way, each scyphistoma is like a jellyfish factory, churning out dozens of jellyfish. The summary of jellyfish life cycle can be refer to Fig 1.

Here is a brief description of the entire life cycle of a jellyfish:

Fertilization: Like many other organisms, jellyfish are either male and produce sperm or female and produce eggs. When a male jellyfish is ready to mate, it releases sperm in the water through its mouth. When a female jellyfish passes by, these sperms get attached to her eggs. In her mouth, the process of fertilization occurs. Once the eggs are fertilized, they are either stored on the mother's mouth or in brood pouches along her oral arms. In different species of jellyfish, this process may vary and you may find that the eggs are fertilized in the mother's stomach. In some cases, the unfertilized eggs may be stored in the female's oral arms where they get fertilized by sperm in the water.

Planula Larva: After the embryonic stage, the larvae hatch and get transformed into free-swimming planulae. They then leave the security of their mother's body and set out on their own. A plunula has a small oval shape and has tiny hair on its surface that it beats together for movement. But, just like the adult jellyfish, most of its movements are entirely dependent on water tides and currents. Each planula floats around for a few days near the surface of the water and then sinks towards the ocean bottom.

Polyp (scyphistoma): After a planula sinks to the bottom, it attaches itself to a hard stationary surface. This cylindrical planula is attached to the surface at its base; at its top is its mouth surrounded by a few tentacles which gather food. As this polyp grows, it begins to form new polyps from its trunk, forming a polyp hydroid colony. All the polyp members of this colony are attached to each other by tiny feeding tubes. This entire stage in the life cycle of a jellyfish is a sessile stage, because the polyp colony is stationary and attached to a single surface. These colonies are known to grow to very large sizes and can exist for a number of years. Only after the polyp colony has grown to an appropriate size, will the next stage of the life cycle of a jellyfish begin.

Ephyra and Medusa: When the last stage is reached, the stalk of ployp begins to develop horizontal grooves. The topmost groove will free itself from the stalk as a baby jellyfish, known as ephyra. This ephyra will grow in size and become the adult jellyfish we all recognize. This last stage is the asexual reproduction aspect of the jellyfish's life cycle.

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